Q&A: Meteor Showers and the ISS

Question: Your post last week made me wonder. When we have a meteor shower, does the ISS ever get hit? I read that there are several meteor showers every year. Are the astronauts in any danger up there in the ISS? Also, does the Moon ever get hit by meteors? — JJ, Grade 8, Miami, FL

Answer: Yes, the ISS has been hit. Space is a dangerous place, even without meteor showers. There’s a lot of debris in orbit around Earth at the altitude of the ISS: pieces of satellites that collided, tools “dropped” by astronauts while on a space walk (including one hammer that got away), and leftover components from rocket boosters.

In fact, the ISS has been hit many times, fortunately by relatively small objects that were stopped by the hull or windows. One of the main observing windows currently has a small chip in the outside layer, like what you’d get on the windshield of your car from a piece of gravel. These are thick windows — 10 times thicker than a car’s windshield, and made from four layers of fused silica and borosilicate glass. That window is currently being evaluated for replacement.

Fortunately, the ISS has not been hit (yet) by anything that caused real damage or depressurization. Should that happen, there are well-rehearsed protocols in place to repair any minor punctures, and the ISS carries replacement air onboard in pressurized tanks. They’ve been lucky so far, but it’s only a matter of when, not if, something larger will hit.

If there was anything really large headed their way, say, something large enough to destroy the station, it would be picked up by ground radar (hopefully with sufficient advance warning) and trigger either of two scenarios. The attached Zvezda module (which is kept fueled at all times) can act as a thruster, allowing slight changes in the ISS orbit. If they can’t “dodge the bullet” for whatever reason, the backup plan involves moving the entire crew into the attached Soyuz module (not visible in photo), detaching from the ISS, and returning safely to Earth. Soyuz is their “escape vehicle.”

There’s a good photo of Soyuz here. What look like “wings” in that image are actually solar panels for electrical power. Soyuz has three sections, each containing various mission components. The middle section is the actual “escape vehicle” and is officially known as the descent module. The other two sections would be jettisoned.

So yes, the risk of a hit is greater during a meteor shower. There are about a dozen showers that occur at regular intervals each year around the same dates. And the ISS is a large target — about the size of a football field, but most of that size is from the solar panels that provide electrical power. The modules inhabited by the crew are smaller targets. And even during a meteor shower, the distance between the bigger meteors is substantial.

Finally, you ask if the Moon ever gets hit by meteors. Take a look at the Moon through a telescope (maybe your school has one) and you’ll see thousands of craters made by meteors. Unlike Earth, the Moon has no protective atmosphere, so there’s nothing to deflect or incinerate incoming meteors. They all make it to the surface.

Check out this video showing one impact flash and resultant new crater. Scientists estimate this was a 400 kg boulder that struck with a speed of 25 km/s (56,000 mph). That’s enough energy to vaporize most of the boulder, as well as some lunar surface material, hence the bright flash. It was bright enough to see with the unaided eye from Earth, if you had been looking at the Moon during that brief event. Now that meteor would have done significant damage to the ISS. But in this case, our Moon took the bullet.

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